Communication system, communication method, and data processing apparatus

ABSTRACT

A communication system and communication method enable various types of near field communication. NFC communication apparatuses have two features in that each can perform communication in two communication modes and that each can perform data transmission at a plurality of transfer rates. The two communication modes consist of a passive mode and an active mode. In the passive mode, between the NFC communication apparatuses, for example, a first NFC communication apparatus transmits data to a second NFC communication apparatus by modulating electromagnetic waves generated by itself, while the second NFC communication apparatus transmits data to the first NFC communication apparatus by performing load modulation on the electromagnetic waves generated by the first NFC communication apparatus. Alternatively, in the active mode, either of the NFC communication apparatuses transmits data by modulating electromagnetic waves generated by itself. The present innovation can be applied to, for example, an IC card system, etc.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 14/800,275 filed Jul. 15, 2015which is a continuation of U.S. Ser. No. 14/587,903 filed Dec. 31, 2014,now U.S. Pat. No. 9,106,273, which is a continuation of U.S. Ser. No.13/757,109, filed Feb. 1, 2013, now U.S. Pat. No. 8,942,629, which is acontinuation of U.S. Ser. No. 13/476,673, filed May 21, 2012, now U.S.Pat. No. 8,417,184, which is a continuation of U.S. Ser. No. 11/954,838,filed Dec. 12, 2007, now U.S. Pat. No. 8,224,243, which is acontinuation of U.S. Ser. No. 10/503,936, filed Aug. 16, 2004, now U.S.Pat. No. 7,346,061, which is a National Stage Application ofPCT/JP03/13753 filed Oct. 28, 2003, which is based upon and claimspriority under 35 U.S.C. §119 to Japan Patent Application Nos.2002-364748, filed Dec. 17, 2002, and 2003-307840, filed Aug. 29, 2003.The entire contents of each of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to communication systems, communicationmethods, and data processing apparatuses, and in particular, to acommunication system, a communication method, and a data processingapparatus which enable various types of short-range communication, whichmatch needs, etc.

BACKGROUND ART

For example, an IC (Integrated Circuit) system is widely known as asystem for performing short-range communication. In an IC card system, aso-called RF (Radio Frequency) field is formed such that a reader/writergenerates electromagnetic waves. When an IC card is brought close to thereader/writer, the IC card is supplied with power throughelectromagnetic induction and performs data transfer between it and thereader/writer (see, for example, Japanese Unexamined Patent ApplicationPublication No. 10-13312).

Presently implemented specifications of IC card systems include, forexample, those called Type A, Type B, and Type C.

Type A is employed as the MIFARE method of Philips. For datatransmission from a reader/writer to an IC card, Miller-based dataencoding is performed. For data transmission from an IC card to areader/writer, Manchester-based data encoding is performed. Also, inType A, 106 kbps (kilo bit per second) is employed as a data transferrate.

In Type B, for data transmission from a reader/writer to an IC card,data encoding based on NRZ is performed, while, for data transmissionfrom an IC card to a reader/writer, data encoding based on NRZ-L isperformed. Also, in Type B, 106 kbps is employed as a data transferrate.

Type C is employed as the Felica method of Sony Corporation, the presentApplicant. For data transmission from a reader/writer to an IC card,Manchester-based data encoding is performed. In Type C, 212 kbps isemployed as a data transfer rate.

Accordingly, when considering, for example, the transfer rates, Types A(or B) and C differ in transfer rate. Thus, use of an IC card based onthe other type in a service in which Type A or C is employed isdifficult since users may become confused, etc.

Also, it is expected that IC card systems enabling data transmission at,for example, 424 kbps and 848 kbps will appear. In such a case, it isrequired that compatibility with the existing IC card system beachieved.

In addition, conventionally, a reader/writer transmits data to an ICcard by modulating (a carrier corresponding to) electromagnetic wavesgenerated by the reader/writer, and the IC card transmits data to thereader/writer by performing load modulation on (a carrier correspondingto) electromagnetic waves generated by the IC card. Thus, even if ICcards exchange data, it is required that a reader/writer be providedtherebetween.

However, from now, it is expected that the need for IC cards themselvesto generate electromagnetic waves and to directly exchange data willincrease.

DISCLOSURE OF INVENTION

The present invention is made in view of such circumstances, and enablesvarious types of near field communication.

In a communication system of the present invention: first and seconddata processing apparatuses each comprises: modulating means formodulating a carrier into a signal of data to be transmitted at one of aplurality of transfer rates; and demodulating means for demodulating asignal of data transmitted at one of a plurality of transfer rates; atransfer rate for use between the first and second data processingapparatuses is changeable in one transaction; each apparatus of thefirst and second data processing apparatuses has, as communicationmodes, an active mode in which the apparatus transmits data byoutputting a carrier; and a passive mode in which one data processingapparatus of the first and second data processing apparatuses transmitsdata by outputting a carrier, while the other data processing apparatustransmits data by performing load modulation on the carrier output bythe one data processing apparatus; and data transmission is performed byusing any communication mode of the active mode and the passive mode,the communication mode being maintained during at least one transaction.

A communication method of the present invention comprises: a selectingstep of selecting, by a first data processing apparatus, a targetapparatus as a communication party from among at least one second dataprocessing apparatus; a transmission-rate determining step ofdetermining a transfer rate for use in data transmission by the firstand second data processing apparatuses from among a plurality oftransfer rates; a changing step of changing a communication parameterconcerning communication between the first data processing apparatus andthe target apparatus; a data exchanging step of, by transmitting acommand to request data exchange by the first data processing apparatus,and transmitting a response to the command by the target apparatus,exchanging data between the first data processing apparatus and thetarget apparatus; and a releasing step of releasing the second dataprocessing apparatus, which is selected as the target apparatus; andbetween two communication modes consisting of an active mode in whichthe first data processing apparatus and the target apparatus themselvesoutput carriers, whereby data is transmitted, and a passive mode inwhich the first data processing apparatus itself outputs a carrier andthe target apparatus performs load modulation on the carrier output bythe first data processing apparatus, whereby data is transmitted, acommunication mode for use in data transmission by the first dataprocessing apparatus and the target apparatus is set.

In a first data processing apparatus of the present invention, amodulating means transmits data at a plurality of transfer rates, andidentifies a communication party, based on a response sent back for datatransmission at each of the transfer rates, and, in addition, determinesa transfer rate for use in data transmission with the communicationparty.

In a second data processing apparatus of the present invention, amodulating means performs data transmission with a communication partyby transmitting, to the communication party, a response to a commandwhich is acquired after being transmitted from the communication party,and a demodulating means performs demodulation at a plurality oftransfer rates, and determines, from among the transfer rates, thetransfer rate of data capable of being demodulated by the demodulatingmeans, as a transfer rate for use in data transmission with thecommunication party.

In a communication system of the present invention, a carrier ismodulated into a signal of data to be transmitted at one of a pluralityof transfer rates, and a signal of data transmitted at one of aplurality of transfer rates is demodulated. A transfer rate for usebetween first and second data processing apparatuses is changeable inone transaction. The first and second data processing apparatuses eachhave, as communication modes, an active mode in which the apparatustransmits data by outputting a carrier; and a passive mode in which onedata processing apparatus of the first and second data processingapparatuses transmits data by outputting a carrier, while the other dataprocessing apparatus transmits data by performing load modulation on thecarrier output by the one data processing apparatus. Data is transmittedby using any communication mode of the active mode and the passive mode,the communication mode being maintained during at least one transaction.

In a communication method of the present invention, a first dataprocessing apparatus selects a target apparatus as a communication partyfrom among at least one second data processing apparatus, and, among aplurality of transfer rates, a transfer rate for use in datatransmission between the first and second data processing apparatuses isdetermined. In addition, after a communication parameter concerning thecommunication between the first data processing apparatus and the targetapparatus is changed, the first data processing apparatus transmits acommand to request data exchange, and the target apparatus transmits aresponse to the command, whereby data exchange is performed between thefirst data processing apparatus and the target apparatus. Between twocommunication modes consisting of an active mode in which the first dataprocessing apparatus and the target apparatus themselves outputcarriers, whereby both apparatuses transmit data, and a passive mode inwhich the first data processing apparatus itself outputs a carrier andthe target apparatus performs load modulation on the carrier output bythe first data processing apparatus, whereby both apparatuses transmitdata, a communication mode for use in data transmission by the firstdata processing apparatus and the target apparatus is set.

A first data processing apparatus of the present invention transmitsdata at a plurality of transfer rates, and, based on a response sentback for data transmission at each of a plurality of transfer rates,identifies a communication party. In addition, among a plurality oftransfer rates, a transfer rate for use in data transmission with thecommunication party is determined.

A second data processing apparatus of the present invention transmits aresponse to a command which is acquired by a demodulating means afterbeing transmitted from a communication party, whereby data transmissionwith the communication party is performed. Also, demodulation at aplurality of transfer rates is performed, and, among a plurality oftransfer rates, the transfer rate of data capable of being demodulatedis determined as a transfer rate for use in data transmission with thecommunication party.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the configuration of an embodiment of acommunication system to which the present invention is applied.

FIG. 2 is an illustration of a passive mode.

FIG. 3 is an illustration of an active mode.

FIG. 4 is a block diagram showing an example of an NFC communicationapparatus 1.

FIG. 5 is a block diagram showing an example of a demodulating unit 13.

FIG. 6 is a block diagram showing an example of a modulating unit 19.

FIG. 7 is a block diagram showing another example of the demodulatingunit 13.

FIG. 8 is a block diagram showing an example of still another example ofthe demodulating unit 13.

FIG. 9 is a timing chart illustrating initial RFCA processing.

FIG. 10 is a timing chart illustrating active RFCA processing.

FIG. 11 is an illustration of SDD processing.

FIG. 12 is an illustration of a list of commands and responses.

FIG. 13 is a flowchart illustrating a process of an NFC communicationapparatus.

FIG. 14 is a flowchart showing a passive-mode-initiator process.

FIG. 15 is a flowchart showing a passive-mode-target process.

FIG. 16 is a flowchart showing a process of an active-mode-initiatorprocess.

FIG. 17 is a flowchart showing a process of an active-mode-targetprocess.

FIG. 18 is a flowchart showing a passive-mode-initiator communicationprocess.

FIG. 19 is a flowchart showing a passive-mode-initiator communicationprocess.

FIG. 20 is a flowchart showing a passive-mode-target communicationprocess.

FIG. 21 is a flowchart showing an active-mode-initiator communicationprocess.

FIG. 22 is a flowchart showing an active-mode-initiator communicationprocess.

FIG. 23 is a flowchart showing an active-mode-target communicationprocess.

FIG. 24 is a flowchart illustrating common initialization and SDDperformed by an NFC communication apparatus.

FIG. 25 is a flowchart illustrating initialization and SDD performed byan initiator.

FIG. 26 is a timing chart illustrating initialization in an active mode.

FIG. 27 is a flowchart illustrating an activation protocol in a passivemode.

FIG. 28 is a flowchart illustrating an activation protocol in an activemode.

FIG. 29 is an illustration of NFCIP-1 protocol commands and responses tothe commands.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are described below with referenceto the drawings.

FIG. 1 shows the configuration of an embodiment of a communicationsystem (the system represents a body formed by logically connectedapparatuses irrespective of whether or not the configurations of theapparatuses are within a single housing) to which the present inventionis applied.

In FIG. 1, the communication system is constituted by three NFCcommunication apparatuses 1, 2, and 3. The NFC communication apparatuses1 to 3 can perform near field communication (NFC) to one another whichis based on electromagnetic induction and which use carriers having asingle frequency.

Here, as the frequency of the carriers used by the NFC communicationapparatuses 1 to 3, for example, 13.56 MHz in the ISM (IndustrialScientific Medical) band, etc., can be used.

Also, the near field communication represents communication that becomespossible when the distance between communicating apparatuses is withindozens of centimeters, and includes also communication that is performedsuch that (the housings of) communicating apparatuses touch each other.

In the communication system in FIG. 1, among the NFC communicationapparatuses 1 to 3, definitely, at least one can be employed as areader/writer, and another one or more can be employed as an IC cardsystem with them as IC cards. The NFC communication apparatuses 1 to 3can be employed as communication systems such as PDAs (Personal DigitalAssistants), PCs (Personal Computers), cellular phones, and pens. Inother words, the NFC communication apparatuses 1 to 3 are apparatusperforming near field communication, and are not limited to IC cards andreader/writers in an IC card system.

The NFC communication apparatuses 1 to 3 have two features firstly inthat communication is possible in two communication modes, and secondlyin that data transmission based on a plurality of transfer rates ispossible.

The two communication modes consist of a passive mode and an activemode. In the case of paying attention to, for example, communicationbetween the NFC communication apparatuses 1 and 2 among the NFCcommunication apparatuses 1 to 3, in a passive mode, similarly to theabove IC card system of the related art, one NFC communication apparatusbetween the NFC communication apparatuses 1 and 2, for example, the NFCcommunication apparatus 1 transmits data to the NFC communicationapparatus 2, which is the other NFC communication apparatus, bymodulating (a carrier corresponding to) electromagnetic waves that theNFC communication apparatus 1 itself generates, and the NFCcommunication apparatus 2 transmits data to the NFC communicationapparatus 1 by performing load modulation on (the carrier correspondingto) electromagnetic waves that the NFC communication apparatus 1generates.

On the other hand, in an active mode, either apparatus of the NFCcommunication apparatuses 1 and 2 transmits data by modulating (acarrier corresponding to) electromagnetic waves generated by theapparatus.

Here, when near field communication based on electromagnetic inductionis performed, an apparatus that initiates communication by initiallyoutputting electromagnetic waves, so to speak, an apparatus that takescontrol of communication, is called an initiator. Near fieldcommunication is performed in a form in which the initiator transmits acommand to another communication party and the communication party sendsback a response to the command. A communication party that sends back aresponse to a command from the initiator is called a target.

For example, when it is assumed that the NFC communication apparatus 1initiates output of electromagnetic waves to initiate communication withthe NFC communication apparatus 2, as FIG. 2 and FIG. 3 show, the NFCcommunication apparatus 1 is an initiator, and the NFC communicationapparatus 2 is a target.

In the passive mode, as shown in FIG. 2, the NFC communication apparatus1, which is the initiator, continues to output electromagnetic waves,and transmits data to the NFC communication apparatus 2, which is thetarget, by modulating the electromagnetic waves that the NFCcommunication apparatus 1 itself outputs. In addition, the NFCcommunication apparatus 2 transmits data to the NFC communicationapparatus 1 by performing load modulation on the electromagnetic wavesthat the NFC communication apparatus 1, which is the initiator, outputs.

Alternatively, in the active mode, as shown in FIG. 3, when the NFCcommunication apparatus 1, which is the initiator, transmits data, itinitiates output of electromagnetic waves by itself, and transmits datato the NFC communication apparatus 2, which is the target, by modulatingthe electromagnetic waves. The NFC communication apparatus 1 stopsoutputting the electromagnetic waves after ending the transmission ofthe data. When the NFC communication apparatus 2 itself, which is thetarget, transmits data, it initiates output of electromagnetic waves,and transmits data to the NFC communication apparatus 2, which is thetarget, by modulating the electromagnetic waves. The NFC communicationapparatus 2 stops outputting the electromagnetic waves after ending thetransmission of the data.

The second feature that the NFC communication apparatuses 1 to 3 canperform data transmission at a plurality of transfer rates is describedlater.

Although, in FIG. 1, three NFC communication apparatuses 1 to 3constitute the communication system, the NFC communication apparatusesconstituting the communication system are not limited to three, but maybe two, or at least four. In addition, the communication system can beconstituted including, for example, an IC card and reader/writerincluded in the IC card system of the related art, in addition to theNFC communication apparatuses.

Next, FIG. 4 shows an example of the NFC communication apparatus 1 inFIG. 1. A description of the other NFC communication apparatuses 2 and 3in FIG. 1 is omitted since they are also similar in configuration to theNFC communication apparatus 1 in FIG. 4.

An antenna 11 is in the form of a closed loop coil, and outputselectromagnetic waves based on changes in a current flowing in the coil.Changes in magnetic flux through the coil as the antenna 11 cause acurrent to flow in the antenna 11.

A receiving unit 12 receives the current flowing in the antenna 11,performs tuning and detection, and outputs a signal to a demodulatingunit 13. The demodulating unit 13 demodulates the signal supplied fromthe receiving unit 12 and supplies the demodulated signal to a decodingunit 14. The decoding unit 14 decodes the signal supplied from thedemodulating unit 13, for example, a Manchester code or the like, andsupplies a data processing unit 15 with data obtained by the decoding.

The data processing unit 15 performs predetermined processing based onthe data supplied from the decoding unit 14. Also, the data processingunit 15 supplies an encoding unit 16 with data to be transmitted toanother apparatus.

The encoding unit 16 encodes the data supplied from the data processingunit 15 into, for example, a Manchester code, and supplies the code to aselecting unit 17.

The selecting unit 17 selects either a modulating unit 19 or a loadmodulation unit 20, and outputs the signal supplied from the encodingunit 16 to the selected unit.

At this time, under the control of a control unit 21, the selecting unit17 selects the modulating unit 19 or the load modulation unit 20. Thecontrol unit 21 controls the selecting unit 17 to select the loadmodulation unit 20 when the communication mode is a passive mode, andthe NFC communication apparatus 1 is a target. Also, when thecommunication mode is an active mode, or the communication mode is apassive mode and the NFC communication apparatus 1 is an initiator, thecontrol unit 21 controls the selecting unit 17 to select the modulatingunit 19. Accordingly, the signal output by the encoding unit 16 issupplied to the load modulation unit 20 through the selecting unit 17when the communication mode is the passive mode and the NFCcommunication apparatus 1 is the target, and is supplied to themodulating unit 19 through the selecting unit 17 in other cases.

An electromagnetic wave output unit 18 supplies the antenna 11 with acurrent for allowing the antenna 11 to radiate (electromagnetic wavesof) a carrier having a predetermined single frequency. In accordancewith the signal supplied from the selecting unit 17, the modulating unit19 modulates the carrier as the current supplied to the antenna 11 bythe electromagnetic wave output unit 18. This allows the antenna 11 toradiate carrier-modulated electromagnetic waves in accordance with dataoutput to the encoding unit 16 by the data processing unit 15.

The load modulation unit 20 changes, in accordance with the signalsupplied from the selecting unit 17, an impedance obtained when the coilas the antenna 11 is externally observed. When an RF field (magneticfield) is formed around the antenna 11 such that another apparatusoutputs electromagnetic waves as a carrier, the impedance, obtained whenthe coil as the antenna 11 is observed, changes, whereby the RF fieldaround the antenna 11 also changes.

This modulates the carrier as the electromagnetic waves output by theother apparatus in accordance with the signal supplied from theselecting unit 17, and transmits, to the other apparatus outputting theelectromagnetic waves, the data output to the encoding unit 16 by thedata processing unit 15.

Here, for example, Amplitude Shift Keying (ASK) can be employed as amodulation method in the modulating unit 19 and the load modulation unit20. However, the modulation method in the modulating unit 19 and theload modulation unit 20 is not limited to ASK, but PSK (Phase ShiftKeying), QAM (Quadrature Amplitude Modulation), etc., can be employed.

The modulation factor of the amplitude is not limited to numeric values,such as 8% to 30%, 50%, and 100%, but a suitable value may be selected.

The control unit 21 controls blocks constituting the NFC communicationapparatus 1. A power supply unit 22 supplies necessary power to theblocks constituting the NFC communication apparatus 1. In FIG. 4,representation of lines showing that the control unit 21 controls theblocks constituting the NFC communication apparatus 1, andrepresentation of lines showing that the load circuit 22 supplies powerto the NFC communication apparatus 1 complicate FIG. 4. Accordingly, therepresentations are omitted.

Although, in the above case, the decoding unit 14 and the encoding unit16 can process the Manchester code as employed in the above Type C, thedecoding unit 14 and the encoding unit 16 can selectively process, notonly the Manchester code, but also one of plural types of codes such asa modified Miller code as employed in Type A and NRZ as employed in TypeC.

Next, FIG. 5 shows an example of the demodulating unit 13 in FIG. 4.

In FIG. 5, the demodulating unit 13 includes a selecting unit 31, Ndemodulating units 32 ₁ to 32 _(N) where N is 2 or greater, and aselecting unit 33.

Under the control of the control unit 21 (FIG. 4), the selecting unit 31selects one demodulating unit 32 _(n) (n=1, 2, . . . , N) from among theN demodulating units 32 ₁ to 32 _(N), and supplies the selecteddemodulating unit 32 _(n) with the signal output by the receiving unit12.

The demodulating unit 32 _(n) demodulates a signal transmitted at then-th transfer rate and supplies the demodulated signal to the selectingunit 33. Here, the demodulating unit 32 _(n) and demodulating unit 32_(n′) (n≠n′) demodulate signals transmitted at different transfer rates.Accordingly, the demodulating unit 13 in FIG. 5 can demodulate signalstransmitted at N transfer rates from the first to the N-th. For example,106 kbps, 212 kbps, 424 kbps, 848 kbps, etc., as described above, can beemployed as the N transfer rates. In other words, the N transfer ratescan include, for example, transfer rates already employed for near fieldcommunication such as the existing IC card systems and the othertransfer rates.

Under the control of the control unit 21, the selecting unit 33 selectsone demodulating unit 32 _(n) from among the N demodulating units 32 ₁to 32 _(N′) and supplies the demodulated output obtained in thedemodulating unit 32 _(n) to the decoding unit 14.

In the demodulating unit 13 having the above-described configuration,the control unit 21 (FIG. 4) controls, for example, the selecting unit31 to sequentially select the N demodulating units 32 ₁ to 32 _(N′)whereby each of the demodulating units 32 ₁ to 32 _(N) is controlled todemodulate the signal supplied from the receiving unit 12 through theselecting unit 31. The control unit 21 recognizes the demodulating unit32 _(n), which has successfully performed normal demodulation of thesignal supplied from the receiving unit 12 through the selecting unit31, and controls the selecting unit 33 to select the output of thedemodulating unit 32 _(n). Under the control of the control unit 21, theselecting unit 33 selects the demodulating unit 32 _(n), whereby thenormal demodulated output obtained in the demodulating unit 32 _(n) issupplied to the decoding unit 14.

Accordingly, the demodulating unit 13 can demodulate a signaltransmitted at an arbitrary transfer rate among the N transfer rates.

Only when the demodulating units 32 ₁ to 32 _(N) have successfullyperformed normal demodulation can they output demodulated outputs, andthey can output nothing (for example, they have high impedance) if theyhave failed to perform normal demodulation. In this case, the selectingunit 33 may output the logical sum of all the outputs of thedemodulating units 32 ₁ to 32 _(N) to the decoding unit 14.

Next, FIG. 6 shows an example of the modulating unit 19 in FIG. 4.

In FIG. 6, the modulating unit 19 includes a selecting unit 41, and Nmodulating units 42 ₁ to 42 _(N) where N is two or greater, and aselecting unit 43.

Under the control of the control unit 21 (FIG. 4), the selecting unit 41selects one modulating unit 42 _(n) (n=1, 2, . . . , N) from among the Nmodulating units 42 ₁ to 42 _(N) and supplies the selected modulatingunit 42 _(n) with a signal output by the selecting unit 17 (FIG. 4).

In accordance with a signal supplied from the selecting unit 41, themodulating unit 42 _(n) modulates the carrier, which is a currentflowing in the antenna 11 after passing through the selecting unit 43,so that data transmission can be performed at the n-th transfer rate.

At this time, the modulating unit 42 _(n) and a modulating unit 42 _(n′)(n≠n′) modulate the carrier at different transfer rates. Accordingly,the modulating unit 19 in FIG. 6 can transmit data at N transfer ratesfrom the first to N-th. As the N transfer rates, transfer ratesidentical to those at which demodulation can be performed by thedemodulating unit 13 in FIG. 5 can be employed.

Under the control of the control unit 21, the selecting unit 43 selects,from among the N modulating units 42 ₁ to 42 _(N), the same modulatingunit 42 _(n) selected by the selecting unit 41, and electricallyconnects the selected modulating unit 42 _(n) and the antenna 11.

In the modulating unit 19 having the above-described configuration, thecontrol unit 21 (FIG. 4) controls, for example, the selecting unit 41 tosequentially selects the N modulating units 42 ₁ to 42 _(N), wherebyeach of the modulating units 42 ₁ to 42 _(N) is controlled to modulate acarrier, which is a current flowing in the antenna 11 after passingthrough the selecting unit 43, in accordance with a signal supplied fromthe selecting unit 41.

Accordingly, the modulating unit 19 can transmit data by modulating thecarrier so that data can be transmitted at an arbitrary rate among the Ntransfer rates.

Since the load modulation unit 20 in FIG. 4 is similar in configurationto, for example, the modulating unit 19 in FIG. 6, its description isomitted.

As described above, the NFC communication apparatuses 1 to 3 canmodulate a carrier to generate a signal of data transmitted at one of Ntransfer rates, and can demodulate the signal of data transmitted at oneof N transfer rates. The N transfer rates can include, for example,transfer rates already employed for near field communication, such asthe existing IC card system (Felica method, etc.), as described above,and other transfer rates. Accordingly, among the NFC communicationapparatuses 1 to 3, one can exchange data with another at any transferrate among the N transfer rates. Moreover, according to the NFCcommunication apparatuses 1 to 3, data can be exchanged even between anIC card and a reader/writer which are included in the existing IC cardsystem at a transfer rate employed by the IC card or reader/writer.

As a result, even if the NFC communication apparatuses 1 to 3 areintroduced into a service employing the existing near fieldcommunication, users do not become confused, etc. Therefore, theintroduction can be easily performed. In addition, the NFC communicationapparatuses 1 to 3 can be easily introduced even to a service whichemploys a high-data-rate near field communication expected to appear inthe future, while achieving coexistence with the existing near fieldcommunication.

Also, the NFC communication apparatuses 1 to 3 can perform datatransmission, not only in a passive mode employed in conventional nearfield communication, but also in an active mode in which they transmitdata by outputting electromagnetic waves. Thus, exchange of data can bedirectly performed, even if another apparatus, such as a reader/writer,is not used.

Next, FIG. 7 shows another example of the demodulating unit 13 in FIG.4. In FIG. 7, portions corresponding to those in the case of FIG. 5 aredenoted by identical reference numerals, and their descriptions areomitted, if needed. Specifically, the demodulating unit 13 in FIG. 7 isbasically similar to that in the case of FIG. 5, excluding a point inwhich the selecting unit 31 is not provided.

In other words, in the embodiment in FIG. 7, the signal output by thereceiving unit 12 is simultaneously supplied to the demodulating units32 ₁ to 32 _(N), and the signal from the receiving unit 12 issimultaneously demodulated by the demodulating units 32 ₁ to 32 _(N).The control unit 21 recognizes, for example, the demodulating unit 32_(n), which has successfully performed normal demodulation of the signalfrom the receiving unit 12, and controls the selecting unit 33 so thatthe demodulating unit 32 _(n) performs output. Under the control of thecontrol unit 21, the selecting unit 33 selects the demodulating unit 32_(n), whereby the normally demodulated output by the demodulating unit32 _(n) is supplied to the decoding unit 14.

In the embodiment in FIG. 7, it is required that the demodulating units32 ₁ to 32 _(N) always perform demodulating operations. Conversely, inthe embodiment in FIG. 5, among the demodulating units 32 ₁ to 32 _(N),only one selected by the selecting unit 31 can perform a demodulatingoperation, and the other ones can stop their operations. Accordingly,from an apparatus-power-consumption saving viewpoint, the configurationin FIG. 5 is more advantageous compared with FIG. 7. Alternatively, froma viewpoint of obtaining a normal demodulated output, the configurationin FIG. 7 is more advantageous compared with FIG. 5.

Next, FIG. 8 shows still another example of the demodulating unit 13 inFIG. 4.

In FIG. 8, the demodulating unit 13 includes a variable ratedemodulating unit 51 and a rate detecting unit 52.

The variable rate demodulating unit 51 demodulates the signal suppliedfrom the receiving unit 12, as a signal having a transfer rate inaccordance with an instruction from the rate detecting unit 52, andsupplies the demodulation result to the decoding unit 14. The ratedetecting unit 52 detects the transfer rate of the signal supplied fromthe receiving unit 12, and instructs the variable rate demodulating unit51 to demodulate the signal having the transfer rate.

In the demodulating unit 51 having the above-described configuration,the signal output by the receiving unit 12 is supplied to the variablerate demodulating unit 51 and the rate detecting unit 52. The ratedetecting unit 52 performs detection about to which one of the Ntransfer rates from the first to the N-th the transfer rate of thesignal supplied from the receiving unit 12 is, and instructs thevariable rate demodulating unit 51 to demodulate the signal having thedetected transfer rate. The variable rate demodulating unit 51demodulates the signal supplied from the receiving unit 12, as a signalhaving a transfer rate in accordance with an instruction from the ratedetecting unit 52, and supplies the demodulation result to the decodingunit 14.

Next, each of the NFC communication apparatuses 1 to 3 can become aninitiator that initiates communication by initially outputtingelectromagnetic waves. In the active mode, the NFC communicationapparatuses 1 to 3 output electromagnetic waves by themselves, even ifthey become initiators or targets.

Therefore, when the NFC communication apparatuses 1 to 3 are close toone another, and among them, at least two apparatuses outputelectromagnetic waves, collision occurs, so that communication cannot beperformed.

Accordingly, each of the NFC communication apparatuses 1 to 3 detectsthe existence of (an RF field caused by) electromagnetic waves fromanother apparatus. Only when the electromagnetic waves do not exist doesthe NFC communication apparatus initiate electromagnetic waves. This canprevent collision. Here, processing that performs detecting theexistence of electromagnetic waves from another apparatus, and, onlywhen the electromagnetic waves do not exist, initiating output ofelectromagnetic waves is called RFCA (RF Collision Avoidance) processingfrom a purpose of preventing collision.

The RFCA processing includes two types, initial RFCA processing that isinitially performed by an NFC communication apparatus (one or more ofthe NFC communication apparatuses 1 to 3 in FIG. 1), which will becomean initiator, and response RFCA processing that is performed duringcommunication in the active mode by an NFC communication apparatus forinitiating output of electromagnetic waves whenever the NFCcommunication apparatus initiates the output. Both the initial RFCAprocessing and the response RFCA processing are identical to each otherin that an apparatus detects the existence of electromagnetic wavescaused by another apparatus before the apparatus initiates output ofelectromagnetic waves, and, only when the electromagnetic waves do notexist does the apparatus initiate the output of the electromagneticwaves. However, the initial RFCA processing and the response RFCAprocessing differ from each other in points such as a time, from a statein which the existence of the electromagnetic waves caused by the otherapparatus is not detected, to timing with which the output ofelectromagnetic waves must be initiated.

Accordingly, the initial RFCA processing is described with reference toFIG. 9.

FIG. 9 shows electromagnetic waves in which output of theelectromagnetic waves is initiated by the initial RFCA processing. InFIG. 9 (similarly in FIG. 10, which is described later), the horizontalaxis indicates a time, and the vertical axis indicates the level ofelectromagnetic waves output by an NFC communication apparatus.

An NFC communication apparatus which will become an initiator alwaysdetects electromagnetic waves caused by another apparatus. When theelectromagnetic waves caused by the other apparatus are notconsecutively detected during time T_(IDT)+n×T_(RFW), the apparatusinitiates output of electromagnetic waves, and initiates transmission(Send Request) of data (including a command) after at least timeT_(IRFG) elapses from the output.

Here, T_(IDT) in time T_(IDT)+n×T_(RFW) is called an initial delay time.When the frequency of a carrier is represented by f_(c), for example, avalue greater than 4096/f_(c) is employed. n is, for example, an integerwhich is not less than 0 and not greater than 3, and is generated byusing random numbers. T_(RFW) is called an RF waiting time, and, forexample, 512/f_(c) is employed. Time T_(IRFG) is called an initialguard-time, and, for example, a value greater than 5 ms is employed.

By employing n, which is a random number, to time T_(IDT)+n×T_(RFW) inwhich electromagnetic waves must not be detected, a possibility that aplurality of NFC communication apparatuses may initiate output ofelectromagnetic waves with the same timing is achieved.

When an NFC communication apparatus uses initial RFCA processing toinitiate output of electromagnetic waves, the NFC communicationapparatus becomes an initiator. Then, when the active mode is set as acommunication mode, the NFC communication apparatus which becomes theinitiator ends transmission of data of itself, and subsequently endsoutput of the electromagnetic waves. Alternatively, when the passivemode is set as a communication mode, the NFC communication apparatuswhich becomes the initiator still continues the output of theelectromagnetic waves which is initiated by the initial RFCA processinguntil it completes communication with a target.

Next, FIG. 10 shows electromagnetic waves in which output ofelectromagnetic waves is initiated by response RFCA processing.

An NFC communication apparatus which will output electromagnetic wavesin the active mode detects electromagnetic waves caused by anotherapparatus. When the electromagnetic waves caused by the other apparatusare consecutively not detected during time T_(ADT)+n×T_(RFW), the NFCcommunication apparatus initiates output of electromagnetic waves, andinitiates transmission (Send Responses) of data after at least timeT_(ARFG) elapses from the output.

Here, n and T_(RFW) in time T_(ADT)+n×T_(RFW) are equal to those in theinitial RFCA processing in FIG. 9. Also, T_(ADT) in T_(ADT)+n×T_(RFW) iscalled an active delay time, and, for example, a value that is not lessthan 768/f_(c) and not greater than 2559/f_(c) is employed. TimeT_(ARFG) is called an active guard time, and, for example, a valuegreater than 1024/f_(c) is employed.

As is clear from FIG. 9 and FIG. 10, in order to initiate output ofelectromagnetic waves by initial RFCA processing, electromagnetic wavesmust not exist during at least the initial delay time T_(IDT). In orderto initiate output of electromagnetic waves by response RFCA processing,electromagnetic waves must not exist during at least the active delaytime T_(ADT).

The initial delay time T_(IDT) is a value greater than 4096/f_(c), whilethe active delay time T_(ADT) is a value that is not less than 768/f_(c)and not greater than 2559/f_(c). Thus, when an NFC communicationapparatus will become an initiator, a state in electromagnetic waves donot exist is required for a time longer than that in the case ofoutputting electromagnetic waves in communication in the active mode.Conversely, when an NFC communication apparatus will outputelectromagnetic waves in communication in the active mode, the NFCcommunication apparatus must output electromagnetic waves without havingso longer time, compared with the case of becoming the initiator, afterthe state in which the electromagnetic waves do not exist occurs. Thisis because of the following reason. In other words, when NFCcommunication apparatuses perform communication in the active mode, oneNFC communication apparatus transmits data by outputting electromagneticwaves by itself, and subsequently stops outputting the electromagneticwaves. The other NFC communication apparatus initiates output ofelectromagnetic waves and transmits data. Thus, in the communication inthe active mode, either NFC communication apparatus may stop outputtingelectromagnetic waves. Accordingly, when an NFC communication apparatuswill become an initiator, in order to confirm that no active modecommunication is not being performed around the NFC communicationapparatus, it is necessary to confirm, for a sufficient time, thatanother apparatus outputs no electromagnetic waves around the NFCcommunication apparatus that will become the initiator.

Conversely, in the active mode, as described above, an initiator outputselectromagnetic waves, whereby data is transmitted to a target. Afterthe initiator stops outputting the electromagnetic waves, the targetinitiates output of electromagnetic waves, whereby data is transmittedto the target.

After that, the initiator initiates output of electromagnetic wavesafter the target stops outputting the electromagnetic waves, wherebydata is transmitted to the initiator. Subsequently, data is similarlyexchanged between the initiator and the target.

Therefore, when an NFC communication apparatus that will become aninitiator exists around an initiator and a target which communicate witheach other in the active mode, if there is a long time after one of theinitiator and the target which communicate with each other in the activemode stops outputting electromagnetic waves until the other oneinitiates output of electromagnetic waves, no electromagnetic wavesexist during the time. Thus, the NFC communication apparatus that willbecome the initiator initiates output of electromagnetic waves byinitial RFCA processing. In this case, the already performed active modecommunication is hindered.

Accordingly, in the response RFCA processing, which is performed in theactive mode communication, electromagnetic waves must be output withoutan elapse of a time after a state in which electromagnetic waves do notexist occurs.

Next, the NFC communication apparatus that will become the initiatorinitiates output of electromagnetic waves by the initial RFCAprocessing, and subsequently transmits data, as described with referenceto FIG. 9. The NFC communication apparatus that will become theinitiator becomes the initiator by initiating output of electromagneticwaves, and an NFC communication apparatus existing at a position closeto the initiator becomes a target. In order for the initiator toexchange data with the target, the target exchanging the data must beidentified. Accordingly, after initiating output of the electromagneticwaves by the initial RFCA processing, the initiator requests an NFCID(NFC Identification) as information identifying each target from atleast one target existing at a position close to the initiator. Thetarget existing at the position close to the initiator transmits, to theinitiator, NFCID identifying itself in response to a request from theinitiator.

The initiator identifies the target based on the NFCID transmitted fromthe target, as described above, and exchanges data with the identifiedtarget. Processing in which an initiator identifies a target existingaround (at a position close to) the initiator based on NFCID of thetarget is called SDD (Single Device Detection) processing.

In the SDD processing, the initiator requests NFCID of the target, andthe requesting is performed such that the initiator transmits a framecalled a polling request frame. When receiving the polling requestframe, the target determines, for example, NFCID based on randomnumbers, and transmits a frame in which the NFCID is located and whichis called a polling response frame. The initiator recognizes the NFCIDof the target by receiving the polling response frame transmitted fromthe target.

In addition, when the initiator requests NFCIDs from targets around it,if plural targets exist around the initiator, two or more of the pluraltargets may simultaneously transmit their NFCIDs. In this case, theNFCIDs transmitted from the two or more targets collide with oneanother, so that the initiator cannot recognize the colliding NFCIDs.

Accordingly, the SDD processing is performed, for example, by a methodusing time slots in order to avoid collision of NFCIDs as much aspossible.

In other words, FIG. 11 shows an SDD processing sequence performed by amethod using time slots. In FIG. 11, it is assumed that five targets #1,#2, #3, #4, and #5 exist around an initiator.

In the SDD processing, the initiator transmits the polling responseframe. After completion of the transmission, time slots at intervals ofpredetermined time T_(s) are set. Time T_(d) is set to, for example,512×64/f_(c), and time T_(s) as the time slot interval is set to, forexample, 256×64/f_(c). Also, the time slots are sequentially (integer)numbered from zero from, for example, the temporally preceding slot,whereby they are identified.

Although FIG. 11 shows four time slots #0, #1, #2, and #3, for example,up to sixteen time slots can be set. The number TSN of time slots, setfor a certain polling response frame, is designated by the initiator,and is transmitted to a target in a form included in the pollingresponse frame.

The target receives the polling response frame transmitted from theinitiator, and recognizes the number TSN of time slots. The target usesrandom numbers to generate integer R in the range of not less than zeroto TSN-1, and transmits a polling response frame in which its NFCID islocated, with timing of time slot #R determined by the integer R.

As described above, based on random numbers, a target determines timeslots used as timing for transmitting polling response frames. Thus,timing with which the targets transmit polling response frames varies.This can avoid collision of the polling response frames transmitted bythe targets as much as possible.

Even if each target determines, based on random numbers, a time slot astiming for transmitting a polling response frame, time slots in whichpolling response frames are transmitted by the targets coincide with oneanother. This may cause collision of the polling response frames. In theembodiment in FIG. 11, a polling response frame of target #4 istransmitted in time slot #0, polling response frames of targets #1 and#3 are transmitted in time slot #1, a polling response frame of target#5 is transmitted in time slot #2, and a polling response frame oftarget #3 is transmitted, so that the collision between targets #1 and#3 occurs.

In this case, the initiator cannot normally receive the polling responseframes of targets #1 and #3 between which the collision occurs.Accordingly, the initiator transmits a polling request frame again. Thisrequests targets #1 and #3 to transmit polling response frames in whichtheir NFCIDs are located. Subsequently, until the initiator recognizesall the NFCIDs of targets #1 to #5 around it, transmission of pollingrequest frames by the initiator and transmission of polling responseframes by the targets are repeatedly performed.

In a case in which, when the initiator transmits a polling request frameagain, all the targets #1 to #5 can send back polling response frames,there is a possibility that two polling response frames may collide witheach other. Accordingly, in a case in which, after each target receivesa polling request frame from the initiator, the target receives apolling request frame again without taking much time, for example, thetarget can ignore the polling request frame. However, in this case, inthe embodiment in FIG. 11, regarding targets #1 and #3, in which pollingresponse collision occurs for the initially transmitted polling requestframe, the initiator cannot recognize the NFCIDs of targets #1 and #3.Thus, data exchange cannot be performed between targets #1 and #3.

Accordingly, targets #2, #4, and #5, in which their polling responseframes are normally received and their NFCIDs can be recognized, aretemporarily excluded from parties among which communication isperformed, whereby a polling response frame as a response to the pollingrequest frame cannot be sent back. In this case, those which send backpolling response frames to the polling request frame re-transmitted bythe initiator are only targets #1 and #3, whose NFCIDs cannot berecognized through the transmission of the initial polling requestframe. Therefore, in this case, all the NFCIDs of targets #1 to #5 canbe recognized while reducing a possibility that polling response framesmay collide with each other.

In addition, here, when receiving a polling request frame, as describedabove, the target determines (generates) its NFCID based on randomnumbers. Accordingly, from different targets, polling response frameswith identical NFCIDs located therein may be transmitted to theinitiator. When the initiator receives, in different time slots, thepolling response frames with identical NFCIDs located therein, theinitiator can re-transmit a polling request frame, for example,similarly to a case in which polling response frames collide with eachother.

As described above, according to NFC communication apparatuses, evenbetween an IC card and a reader/writer constituting the existing IC cardsystem, data can be exchanged at transfer rates employed by the IC cardand the reader/writer. When a target is, for example, an IC card in theexisting IC card system, SDD processing is performed in, for example,the following manner.

Specifically, an initiator uses the initial RFCA processing to initiateelectromagnetic waves, and an IC card as a target obtains power from theelectromagnetic waves and initiates processing. In other words, in thiscase, the target generates operating power from the electromagneticwaves output by the initiator since it is an IC card in the existing ICcard system.

After obtaining the power and being operable, the target prepares forreceiving a polling request frame within, for example, a maximum of 2seconds, and waits for the polling request frame to be transmitted fromthe initiator.

In addition, the initiator can transmit a polling request frameregardless of whether or not the preparation for receiving the pollingrequest frame is completed in the target.

When the target receives the polling request frame from the initiator,as described above, it transmits a polling response frame to theinitiator with timing of a predetermined time slot. When the initiatorsuccessfully receives the polling response frame from the target, asdescribed above, it recognizes the NFCID of the target. Also, when theinitiator fails to normally receive the polling response frame from thetarget, it can re-transmit a polling request frame.

In this case, the target generates operating power from electromagneticwaves output by the initiator since it is an IC card in the existing ICcard system. Accordingly, the initiator continues to the electromagneticwave output initiated by the initial RFCA processing until communicationwith the target completely ends.

Next, according to NFC communication apparatuses, communication isperformed such that an initiator transmits a command to a target, andthe target transmits (sends back) a response to the command from theinitiator.

Accordingly, FIG. 12 shows commands that the initiator transmits to thetarget, and responses that the target transmits to the initiator.

In FIG. 12, those having the characters REQ after the underbar (_)represent commands, and those having the characters RES after theunderbar (_) represent responses. In the embodiment in FIG. 12, sixtypes of commands, ATR_REQ, WUP_REQ, PSL_REQ, DEP_REQ, DSL_REQ, andRLS_REQ, are available. Similarly to the commands, also six types ofresponses, ATR_RES, WUP_RES, PSL_RES, DEP_RES, DSL_RES, and RLS_RES, areavailable. As described above, an initiator transmits a command(request) to a target, and the target transmits to the initiator aresponse to the command. Accordingly, the command is transmitted by theinitiator, and the response is transmitted by the target.

The command ATR_REQ is such that the initiator notifies the target ofits attributes (specifications) and is transmitted to the target whenthe initiator requests target's attributes. Here, the attributes of theinitiator or the target include the transfer rate of data that can betransmitted or received by the initiator or the target. In the commandATR_REQ, in addition to initiator's attributes, an NFCID identifying theinitiator is located, and the target recognizes the initiator'sattributes and NFCID by receiving the ATR_REQ.

The response ATR_RES is transmitted as a response to the command ATR_REQto the initiator when the target receives the command ATR_REQ. In theresponse ATR_RES, attributes, an NFCID, etc., of the target are located.

Transfer rate information as an attribute located in the command ATR_REQand the response ATR_RES can include all the transfer rates of dataitems which can be transmitted and received by the initiator and thetarget. In this case, by exchanging the command ATR_REQ and the responseATR_RES once between the initiator and the target, the initiator canrecognize a transfer rate at which the target can perform transmissionand reception, and the target can also recognize a transfer rate at theinitiator can perform transmission and reception.

The command WUP_REQ is transmitted when the initiator selects a targetwith which the initiator will communicate. Specifically, by transmittingthe command DSL_REQ, which is described later, from the initiator to thetarget, the target can set to be in a deselect state (a state in whichtransmission (response) of data to the initiator is prohibited). Thecommand WUP_REQ is transmitted in the case of releasing the deselectstate and setting the target to be in a state capable of transmittingdata to the initiator. In the command WUP_REQ, the NFCID of the targetwhose deselect state is to be released is located. Among targets whichreceive the command WUP_REQ, a target which is identified by the NFCIDlocated in the received command WUP_REQ releases its deselect state.

When, among the targets which receive the command WUP_REQ, the targetwhich is identified by the NFCID located in the received command WUP_REQreleases its deselect state, the response WUP_RES is transmitted as aresponse to the command WUP_REQ.

The command PSL_REQ is transmitted when the initiator changescommunication parameters concerning communication with the target. Here,the communication parameters include, for example, the transfer rate ofdata exchanged between the initiator and the target.

The command PSL_REQ includes a changed communication parameter locatedtherein, and is transmitted from the initiator to the target. The targetreceives the command PSL_REQ, and changes its communication parameter inaccordance with the communication parameter located in the command. Thetarget further transmits the response PSL_RES to the command PSL_REQ.

The command DEP_REQ is transmitted when the initiator performstransmission and reception (data exchange with the target) of data(so-called real data). In this command, data to be transmitted to thetarget is located. The response DEP_RES is transmitted as a response tothe command DEP_REQ. In this command, data to be transmitted to theinitiator is located. Accordingly, the command PEP_REQ transmits datafrom the initiator to the target, and the response PEP_RES to thecommand DEP_REQ transmits data from the target to the initiator.

The command DSL_REQ is transmitted when the initiator sets the target tobe in the deselect state. The target, which receives the commandDSL_REQ, transmits the response DSL_RES to the command DSL_REQ beforeentering the deselect state, and subsequently becomes less responsive(comes to send back no response) to commands other than the commandWUP_REQ.

The command RLS_REQ is transmitted when the initiator completely endsthe communication with the target. The target, which received thecommand RLS_REQ, transmits the response RLS_RES to the command RLS_REQ,and completely ends the communication with the initiator.

Here, both the commands DSL_REQ and RLS_REQ are common in excluding atarget from parties communicating with the initiator. However, thetarget excluded by the command DSL_REQ is set to be communicatable withthe initiator again by the command WUP_REQ, while the target excluded bythe command RLS_REQ does not become communicatable with the initiatorunless exchange with the initiator of the above-described pollingrequest frame and polling response frame is performed. In that point,the commands DSL_REQ and RLS_REQ differ from each other.

Exchange of a command and a response is performed in, for example, atransport layer.

Next, a communication process of an NFC communication apparatus isdescribed with reference to the flowchart in FIG. 13.

When initiating communication, in step S1, an NFC communicationapparatus determines whether to have detected electromagnetic wavescaused by another apparatus.

At this time, in the NFC communication apparatus (FIG. 4), for example,the receiving unit 12 monitors the level of a signal output to thedemodulating unit 13 by the receiving unit 12. In step S1, based on thelevel, it is determined whether the electromagnetic waves caused by theother apparatus have been detected.

If the process has determined in step S1 that it has not detected theelectromagnetic waves caused by the other apparatus, it proceeds to stepS2. The NFC communication apparatus sets its communication mode to thepassive mode or the active mode, and performs an initiator process inpassive mode or an initiator process in active mode, which is describedlater. The NFC communication apparatus returns to step S1 after endingthe process, and subsequently repeats similar processing.

Here, in step S2, the communication mode of the NFC communicationapparatus may be set to either the passive mode or the active mode.However, when the target can be only a passive mode target such as an ICcard in the existing IC card system, in step S2, the NFC communicationapparatus needs to set its communication mode to the passive mode and toperform the initiator process in passive mode.

Alternatively, if it is determined that the electromagnetic waves causedby the other apparatus have been detected, that is, when theelectromagnetic waves caused by the other apparatus have been detectedaround the NFC communication apparatus, the NFC communication apparatusproceeds to step S3, and determines whether the electromagnetic wavesdetected in step S1 have been continuously detected.

If the NFC communication apparatus has determined in step S3 that theelectromagnetic waves have been continuously detected, it proceeds tostep S4, and sets its communication mode to the passive mode and atarget process in passive mode, which is described later. In otherwords, the continuous detection of the electromagnetic waves is, forexample, a case in which another apparatus close to the NFCcommunication apparatus is an initiator in passive mode and continues tooutput electromagnetic waves in which the output of the electromagneticwaves is initiated by initial RFCA processing, so that the NFCcommunication apparatus becomes a target in passive mode and performsprocessing. After ending the processing, the NFC communication apparatusreturns to step S1 and subsequently repeats similar processing.

Also, if the NFC communication apparatus has determined in step S3 thatthe electromagnetic waves have not been continuously detected, itproceeds to step S5, and the NFC communication apparatus sets itscommunication mode to the active mode and performs the target process inactive mode, which is described later.

In other words, no continuous detection of the electromagnetic waves is,for example, a case in which another apparatus close to the NFCcommunication apparatus becomes an initiator in active mode andinitiates electromagnetic waves by initial RFCA processing, andsubsequently stops outputting the electromagnetic waves. Accordingly,the NFC communication apparatus becomes a target in active mode andperforms processing. After ending the processing, the NFC communicationapparatus returns to step S1 and subsequently repeats similarprocessing.

Next, the passive-mode initiator process by the NFC communicationapparatus is described with reference to the flowchart in FIG. 14.

In the passive-mode initiator process, at first, in step S11, the NFCcommunication apparatus initiates output of electromagnetic waves. StepS11 in the passive-mode initiator process is performed when theelectromagnetic waves have not been detected in step S1 in the aboveFIG. 13. In other words, when the electromagnetic waves have not beendetected in step S1 in FIG. 13, the NFC communication apparatusinitiates output of electromagnetic waves in step S11. Accordingly,processing in steps S1 and S11 corresponds to the above-describedinitial RFCA processing.

After that, proceeding to step S12, the NFC communication apparatus setstransmission-rate-representing variable n to, for example, an initialvalue of 1 before proceeds to step S13. In step S13, the NFCcommunication apparatus transmits a polling request frame at the n-thtransfer rate (hereinafter referred to also as the n-th rate, ifneeded), and proceeds to step S14. In step S14, the NFC communicationapparatus determines whether a polling response frame has beentransmitted at the n-th rate from another apparatus.

In step S14, when it is determined that the polling response frame hasnot been transmitted from the other apparatus, that is, for example,when another apparatus close the NFC communication apparatus cannotperform communication at the n-th rate, and a polling response frame inresponse to the polling request frame transmitted at the n-th rate isnot sent back, the NFC communication apparatus skips over steps S15 toS17 and proceeds to step S18.

Also, in step S14, when it is determined that a polling response framehas been transmitted at the n-th rate from the other apparatus, that is,for example, when another apparatus close to the NFC communicationapparatus can perform communication at the n-th rate, and a pollingresponse frame in response to the polling request frame transmitted atthe n-th rate is sent back, the NFC communication apparatus proceeds tostep S15, and recognizes the NFCID of a target in passive mode, with theother apparatus, which has sent back the polling response frame as thetarget, and recognizes the target to be communicatable at the n-th rate.

Here, after the NFC communication apparatus recognizes, in step S15, theNFCID of the passive mode target and the target to be communicatable atthe n-th rate, it (temporarily) determines that the transfer ratebetween it and the target is the n-th rate, and performs communicationwith the target at the n-th rate unless the transfer rate is changed bythe command PSL_REQ.

After that, proceeding to step S16, the NFC communication apparatustransmits the command DSL_REQ at the n-th rate to the target (passivemode target) corresponding to the NFCID recognized in step S15. Afterthis sets the target to be in the deselect state so that the target doesnot respond to polling request frames which are subsequentlytransmitted, the NFC communication apparatus proceeds to step S17.

In step S17, the NFC communication apparatus receives the responseDSL_RES which is sent back for the command DSL_REQ transmitted in stepS16 from a target set to be in the deselect state by the commandDSL_REQ, and proceeds to step S18.

In step S18, the NFC communication apparatus determines whether apredetermined time has elapsed since the transmission of the pollingrequest frame at the n-th rate in step S13. Here, the predetermined timein step S18 can be a time of zero or greater.

If the NFC communication apparatus has determined in step S18 that thepredetermined time has not elapsed since the transmission of the pollingrequest frame at the n-th rate in step S13, it returns to step S13, andrepeatedly performs processing in steps S13 to S18.

In this process, the processing in steps S13 to S18 is repeatedlyperformed, whereby the NFC communication apparatus can receive pollingresponse frames transmitted with types of timing in different timeslots, as illustrated by FIG. 11.

Alternatively, if the NFC communication apparatus has determined in stepS18 that the predetermined time has elapsed since the transmission ofthe polling request frame at the n-th rate in step S13, it proceeds tostep S19, and determines whether variable n is equal to its maximumvalue of N. If the NFC communication apparatus has determined thatvariable n is not equal to the maximum value N, that is, when variable nis less than the maximum value N, it proceeds to step S20 and allowsvariable n to be incremented by 1 before returning to step S13.Subsequently, processing in steps S13 to S20 is repeatedly performed.

Here, the processing in steps S13 to S20 is repeatedly performed,whereby the NFC communication apparatus transmits polling request framesat N transfer rates and receives polling response frames sent back attransfer rates.

Alternatively, if the NFC communication apparatus has determined in stepS19 that variable N is equal to the maximum value N, that is, when theNFC communication apparatus transmits polling request frames at N Ntransfer rates and receives polling response frames sent back attransfer rates, it proceeds to step S21 and performs, as a passive modeinitiator, its communication process (passive-mode-initiatorcommunication process). This passive-mode-initiator communicationprocess is described later.

After the passive-mode-initiator communication process ends, the NFCcommunication apparatus proceeds from step S21 to S22, and stopsoutputting the electromagnetic waves whose output is initiated in stepS11, so that the process ends.

Next, the passive-mode-target process by the NFC communication apparatusis described with reference to the flowchart in FIG. 15.

In the passive-mode-target process, at first, in step S31, the NFCcommunication apparatus sets variable n, which represents a transferrate, to, for example, an initial value of 1, and proceeds to step S32.In step S32, the NFC communication apparatus determines whether apolling request frame has been transmitted at the n-th rate from anotherapparatus which serves as a passive mode initiator.

If the NFC communication apparatus has determined in step S32 that nopolling request frame has been transmitted from the passive modeinitiator, that is, when, for example, another apparatus close the NFCcommunication apparatus cannot perform communication at the n-th rate,and thus cannot transmit a polling request frame at the n-th rate, itproceeds to step S33 and the NFC communication apparatus determineswhether variable n is equal to its maximum value of N. If the NFCcommunication apparatus has determined in step S33 that variable n isnot equal to the maximum value N, that is, when variable n is less thanthe maximum value N, it proceeds to step S34 and allows variable n to beincremented by 1 before returning to step S32. Subsequently, processingin steps S32 to S34 is repeatedly performed.

Alternatively, if the NFC communication apparatus has determined in stepS33 that variable n is equal to the maximum value N, it returns to stepS1 and subsequently repeats the processing in steps S31 to S34. In otherwords, in this process, until a polling request frame which istransmitted at any one of the N transfer rates can be received, theprocessing in steps S31 to S34 is repeatedly performed.

If it is determined in step S32 that a polling request frame has beentransmitted from a passive mode initiator, that is, when the NFCcommunication apparatus normally receives a polling request frame at then-th rate, it proceeds to step S35, and the NFC communication apparatusdetermines that the transfer rate between initiators is the n-th rate,and generates its NFCID based on random numbers before proceeding tostep S36. In step S36, the NFC communication apparatus transmits apolling response frame in which its NFCID is located, at the n-th rate,and proceeds to step S37.

Here, after the NFC communication apparatus transmits the pollingresponse frame at the n-th rate in step S36, it performs communicationat the n-th rate unless it is instructed to change the transfer ratesuch that the command PSL_REQ is transmitted from the passive modeinitiator.

In step S37, the NFC communication apparatus determines whether thecommand DSL_REQ has been transmitted from the passive mode initiator,and has determined that the command has not been transmitted, it returnsto step S37 and waits for the command DSL_REQ to be transmitted from thepassive mode initiator.

Also, when it is determined in step S37 that the command DSL_REQ hasbeen transmitted from the passive mode initiator, that is, when the NFCcommunication apparatus receives the command DSL_REQ, the NFCcommunication apparatus proceeds to step S38. It transmits the responseDSL_RES to the command DSL_REQ, and enters the deselect state beforeproceeding to step S39.

In step S39, the NFC communication apparatus performs, as a passive modetarget, its communication process (passive-mode-target communicationprocess). After it ends the passive-mode-target communication process,the process ends. The passive-mode-target communication process isdescribed later.

Next, the active-mode-initiator process by the NFC communicationapparatus is described with reference to the flowchart in FIG. 16.

In the active-mode-initiator process, in each of steps S51 to S61,processing similar to that in each of steps S11 to S21 in thepassive-mode initiator process in FIG. 14 is performed. In thepassive-mode initiator process in FIG. 14, the NFC communicationapparatus continues outputting electromagnetic waves until the processends. The active-mode-initiator process differs in that only when theNFC communication apparatus transmits data does it outputelectromagnetic waves.

In other words, in step S51, the NFC communication apparatus initiatesoutput of electromagnetic waves. Step S51 in the active-mode-initiatorprocess is performed when, in step S1 in the above FIG. 13, theelectromagnetic waves are not detected. Specifically, in step S1 in FIG.13, the NFC communication apparatus initiates output of electromagneticwaves in step S51 when the electromagnetic waves are not detected.Accordingly, processing in steps S1 and S51 corresponds to the aboveinitial RFCA processing.

After that, proceeding to step S52, the NFC communication apparatus setsvariable n, which represents a transfer rate, to, for example, aninitial value of 1, and proceeds to step S53. In step S53, the NFCcommunication apparatus transmits a polling request frame at the n-thrate and stops outputting the electromagnetic waves (hereinafterreferred to also as performing RF-off process, if needed), and proceedsto step S54.

Here, in step S53, before transmitting the polling request frame, theNFC communication apparatus uses the above-described active RFCAprocessing to initiate the output of the electromagnetic waves. However,when variable n is the initial value of 1, the active RFCA processingdoes not need to be performed since the output of the electromagneticwaves has already been initiated by initial RFCA processingcorresponding to the processing in steps S1 and S51.

In step S54, the NFC communication apparatus determines whether apolling response frame has been transmitted at the n-th rate fromanother apparatus.

When it is determined in step S54 that the polling response frame hasnot been transmitted from the other apparatus, that is, for example,when another apparatus close to the NFC communication apparatus cannotperform communication at the n-th rate, and a polling response frame tothe polling request frame transmitted at the n-th rate is not sent back,the NFC communication apparatus skips over steps S55 to S57 and proceedsto step S58.

Also, when it is determined in step S54 that the polling response framehas been transmitted at the n-th rate from the other apparatus, that is,for example, when another apparatus close to the NFC communicationapparatus cannot perform communication at the n-th rate, a pollingresponse frame to the polling request frame transmitted at the n-th rateis sent back, the NFC communication apparatus proceeds to step S55. theNFC communication apparatus regards the other apparatus, which sendsback the polling response frame, as an active mode target, recognizesthe NFCID of the target based on an NFCID located in the pollingresponse frame, and recognizes the target to be communicatable at then-th rate.

When, in step S55, the NFC communication apparatus recognizes the NFCIDof the active mode target and the target to be communicatable at then-th rate, it determines that the transfer rate between it and thetarget is the n-th rate, and performs communication with the target atthe n-th rate unless the transfer rate is changed by the commandPSL_REQ.

After that, proceeding to step S56, the NFC communication apparatusinitiates output of electromagnetic waves by the active RFCA processing,and transmits the command DSL_REQ at the n-th rate to the target (activemode target) having the NFCID recognized in step S55. This sets thetarget to be in a deselect state of not responding to polling responseframes which are subsequently transmitted. After that, the NFCcommunication apparatus performs the RF-off processing, and proceedsfrom step S56 to S57.

In step S57, the NFC communication apparatus receives the responseDSL_RES which is sent back for the command DSL_REQ transmitted in stepS56 from the target set to be in the deselect state by the commandDSL_REQ, and proceeds to step S58.

In step S58, the NFC communication apparatus determines whether apredetermined time has elapsed from the transmission of the pollingrequest frame at the n-th rate in step S53.

When it is determined in step S58 that the predetermined time has notelapsed yet from the transmission of the polling request frame at then-th rate in step S53, the process returns to step S53. Subsequently,processing in steps S53 to S58 is repeatedly performed.

Alternatively, when it is determined in step S58 that the predeterminedtime has elapsed from the transmission of the polling request frame atthe n-th rate in step S53, the NFC communication apparatus proceeds tostep S59 and determines whether variable n is equal to its maximum valueof N. When it is determined in step S59 that variable n is not equal tothe maximum value N, that is, when variable n is less the maximum valueN, the NFC communication apparatus proceeds to step S60 and allowsvariable n to be incremented by 1 before returning to step S53.Subsequently, processing in steps S53 to S60 is repeatedly performed.

Here, the processing in steps S53 to S60, whereby the NFC communicationapparatus transmits polling request frames at N transfer rates andreceives polling response frames sent back at transfer rates.

Alternatively, when it is determined in step S59 that variable n isequal to the maximum value N, that is, when the NFC communicationapparatus transmits polling request frames at N N transfer rates andreceives polling response frames sent back at transfer rates, the NFCcommunication apparatus proceeds to step S61, performs, as an activemode initiator, its communication process (the active-mode-initiatorcommunication process), and subsequently ends the process. Thisactive-mode-initiator communication process is described later.

Next, an active-mode-target process by the NFC communication apparatusis described with reference to the flowchart in FIG. 17.

In the active-mode-target process, in each of steps S71 to S79,processing similar to the case of steps S31 to S39 in the passive-modeis performed. Although, in the passive-mode-target process in FIG. 15,the NFC communication apparatus transmits data by performing loadmodulation on the electromagnetic waves output by the passive modeinitiator, the active-mode-target process differs in that the NFCcommunication apparatus transmits data by outputting electromagneticwaves by itself.

In other words, in the active-mode-target process, in each of steps S71to S75, processing similar to the case of the steps S31 to S35 in FIG.15 is performed.

After processing in step S75, the NFC communication apparatus proceedsto step S76, initiates output of electromagnetic waves by the activeRFCA processing, and transmits a polling response frame in which itsNFCID is located, at the n-th rate. In step S76, the NFC communicationapparatus performs RF-off processing and proceeds to step S77.

Here, after transmitting the polling response frame at the n-th rate instep S76, the NFC communication apparatus performs communication at then-th rate unless the command PSL_REQ is transmitted from the active-modeinitiator to instruct the NFC communication apparatus to change thetransfer rate.

In step S77, the NFC communication apparatus determines whether thecommand DSL_REQ has been transmitted from the active mode initiator. Ifthe NFC communication apparatus has determined that the command has notbeen transmitted, it returns to step S77 and waits for the commandDSL_REQ to be transmitted from the active mode initiator.

Alternatively, if the NFC communication apparatus has determined in stepS77 that the command DSL_REQ has not been transmitted from the activemode initiator, that is, when the NFC communication apparatus hasreceived the DSL_REQ, it proceeds to step S78, initiates output ofelectromagnetic waves by the active RFCA processing, and transmits theresponse DSL_RES to the command DSL_REQ. Also, in step S78, the NFCcommunication apparatus performs RF-off processing and becomes adeselect state before proceeding to step S79.

In step S79, the NFC communication apparatus performs, as an active modetarget, its communication process (active-mode-target communicationprocess). When the active-mode-target communication process ends, theNFC communication apparatus ends its process. The active-mode-targetcommunication process is described later.

Next, the passive-mode-initiator communication process in the step S21in FIG. 14 is described with reference to the flowcharts in FIG. 18 andFIG. 19.

The NFC communication apparatus, which is a passive mode initiator,selects an apparatus (hereinafter referred to as an apparatus ofinterest, if needed) with which it will communicate, from among thetargets having NFCIDs recognized in step S15 in FIG. 14, and proceeds tostep S92. In step S92, it transmits the command WUP_REQ to the apparatusof interest, whereby, by transmitting the command DSL_REQ in step S16 inFIG. 14, the deselect state of the apparatus of interest, which has beenset to be in the deselect state, is released (hereinafter referred to aswaked up, if needed).

Subsequently, after the NFC communication apparatus waits for theapparatus of interest to transmit the response WUP_RES to the commandWUP_REQ, it proceeds from step S92 to S93 and receives the responseWUP_RES before proceeding to step S94. In step S94, the NFCcommunication apparatus transmits the command ATR_REQ to the apparatusof interest. After the NFC communication apparatus waits for theapparatus of interest to transmit the response ATR_RES to the commandATR_REQ, it proceeds from step S94 to S95 and receives the responseATR_RES.

As described above, the NFC communication apparatus and the apparatus ofinterest exchange the command ATR_REQ, in which an attribute is located,and the response ATR_REQ, whereby the NFC communication apparatus andthe apparatus of interest recognize a transfer rate at which both cancommunicate with each other.

After that, proceeding from step S95 to S96, the NFC communicationapparatus transmits the command DSL_REQ to set the apparatus of interestto be in the deselect state. After the NFC communication apparatus waitsfor the apparatus of interest to transmit the response DSL_RES to thecommand DSL_REQ, it proceeds from step S96 to S97 and receives theresponse DSL_RES before proceeding to step S98.

In step S98, the NFC communication apparatus determines whether to haveselected all the targets having NFCIDs recognized in step S15 in FIG.14, as apparatuses of interest, in step S91. If the NFC communicationapparatus has determined in step S98 that some targets have not beenselected as apparatuses of interest yet, it returns to step S91, andselect, as an apparatus of interest, one of the targets which have notbeen selected as apparatuses of interest yet. Subsequently, similarprocessing is repeated.

Alternatively, if the NFC communication apparatus has determined in stepS98 that, in step S91, it has selected, as apparatuses of interest, allthe targets having the NFCIDs recognized in step S15 in FIG. 14, thatis, when the NFC communication apparatus exchanges the command ATR_REQand the response ATR_RES with all the targets having the NFCIDsrecognized, and this enables each target to recognize a communicatabletransfer rate, etc., it proceeds to step S99. The NFC communicationapparatus selects an apparatus (apparatus of interest) with which theNFC communication apparatus will communicate, from among the targetswith which the NFC communication apparatus exchanges the command ATR_REQand the response AIR RES, and proceeds to step S100.

In step S100, the NFC communication apparatus transmits the commandWUP_REQ, and this transmits the command DSL_REQ in step S96, whereby theapparatus of interest, which is set to be in the deselect state, iswaked up. The NFC communication apparatus waits for the apparatus ofinterest to transmit the response WUP_RES to the command WUP_REQ, andproceeds from step S100 to S101. It receives the response WUP_RESthereto and proceeds to step S111 in FIG. 19.

In step S111, the NFC communication apparatus determines whether tochange a communication parameter, such as a transfer rate, in the caseof communicating with the apparatus of interest.

Here, the NFC communication apparatus has received the response ATR_RESin step S95 in FIG. 18, and recognizes, based on the attribute locatedin the response ATR_RES, the communication parameter such as a transferrate at the apparatus of interest can perform communication. When theNFC communication apparatus can communicate with, for example, theapparatus of interest, at a transfer rate higher than the presenttransfer rate, it determines in step S111 to change the communicationparameter in order to change the transfer rate to the higher transferrate. Also, when the NFC communication apparatus can communicate with,the apparatus of interest, at a transfer rate lower than the presenttransfer rate, and the present communication environments have highnoise level, the NFC communication apparatus determines in step S111 tochange the communication parameter so that the transfer rate is changedto a lower transfer rate in order to lower transmission error. Even ifcommunication is possible at a transfer rate different from the presenttransfer rate between the NFC communication apparatus and the apparatusof interest, the communication can be continued with the presenttransfer rate unchanged.

When it is determined in step S111 that the communication parameter inthe case of communicating with the apparatus of interest, that is, whenthe communication is continued between the NFC communication apparatusand the apparatus of interest with the present communication parameterunchanged, the NFC communication apparatus skips over steps S112 to S114and proceeds to step S115.

If the NFC communication apparatus has determined in step S111 to changethe communication parameter in the case of communicating with theapparatus of interest, it proceeds to step S112, and locates the changedcommunication parameter in the command PSL_REQ, and transmits thecommand to the apparatus of interest. The NFC communication apparatuswaits for the apparatus of interest to transmit the response PSL_RES tothe command PSL_REQ before proceeding from step S112 to S113, andreceives the response PSL_RES before proceeding to step S114.

In step S114, the NFC communication apparatus changes the communicationparameter, such as the transfer rate in the case of communicating withthe apparatus of interest, to the value of the communication parameterlocated in the command PSL_REQ transmitted in step S112. After that, theNFC communication apparatus communicates with the apparatus of interestin accordance with the communication parameter, such as the transferrate changed in value in step S114 unless it exchanges the commandPSL_REQ and the response PSL_RES.

According to the exchange (negotiation) of the command PSL_REQ and theresponse PSL_RES, in addition to the transfer rate, for example, theencoding method in the encoding unit 16 (the decoding unit 14), themodulating methods in the modulating unit 19 and the load modulationunit 20 (the demodulating unit 13), etc., can be changed.

After that, the NFC communication apparatus proceeds to step S115 anddetermines whether there is data to be transmitted to and received fromthe apparatus of interest. If it has determined that there is no data,it skips over steps S116 and S117 and proceeds to step S118.

If the NFC communication apparatus has determined in step S115 thatthere is data to be transmitted to or received from the apparatus ofinterest, it proceeds to step S116 and transmits the command DEP_REQ tothe apparatus of interest. Here, in step S116, when there is data to betransmitted to the apparatus of interest, the NFC communicationapparatus transmits the data in a form located in the command DEP_REQ.

The NFC communication apparatus waits for the apparatus of interest totransmit the response DEP_RES to the command DEP_REQ, proceeds from stepS116 to S117, and receives the response DEP_RES before proceeding tostep S118.

As described above, the command DEP_REQ and the response DEP_RES areexchanged between the NFC communication apparatus and the apparatus ofinterest, whereby transmission and reception of so-called real data areperformed.

In step S118, the NFC communication apparatus determines to change thecommunication party. If the NFC communication apparatus has determinedin step S118 not to change the communication party, that is, when thereis still data to be exchanged with, for example, the apparatus ofinterest, it returns to step S111 and subsequently repeats similarprocessing.

Alternatively, if the NFC communication apparatus has determined in stepS118 to change the communication party, that is, for example, when thereis not data to be exchanged with the apparatus of interest, but there isdata to be exchanged with another communication party, it proceeds tostep S119 and transmits the command DSL_REQ or RLS_REQ to the apparatusof interest. the NFC communication apparatus waits for the apparatus ofinterest to transmit the response DSL_RES or RLS_RES to the commandDSL_REQ or RLS_REQ, proceeds from step S119 to S120, and receives theresponse DSL_RES or RLS_RES.

As described above, the NFC communication apparatus transmits thecommand DSL_REQ or RLS_REQ to the apparatus of interest, whereby thetarget as the apparatus of interest is released from targetedapparatuses in communication with the NFC communication apparatus as theinitiator. However, a target released by the command DSL_REQ is set tobe communicatable with the initiator again by the command WUP_REQ, but atarget released by the command RLS_REQ is not set to be communicatablewith the initiator unless it exchanges the above polling request frameand polling response frame with the initiator.

Cases in which a certain target is released from targeted apparatuses incommunication with the initiator include, not only a case in which, asdescribed above, the command DSL_REQ or RLS_REQ is transmitted from theinitiator to the target, but also, for example, a case in which nearfield communication cannot be performed since the initiator and thetarget are too far from each other. In this case, similarly to thetarget released by the command RLS_REQ, the target is not set to becommunicatable with the initiator unless the target exchanges the abovepolling request frame and polling response frame with the initiator.

Here, release of a target which is not set to be communicatable with theinitiator unless the target and the initiator exchange the pollingrequest frame and the polling response frame is hereinafter referred toas complete release. Also, release of target which is set to becommunicatable again with the initiator such that the command WUP_REQ istransmitted by the initiator is temporary release.

After processing in step S120, the NFC communication apparatus proceedsto step S121 and determines whether all the targets having the NFCIDsrecognized in step S15 in FIG. 14 have been released. If the NFCcommunication apparatus has determined in step S121 that all the targetshaving the NFCIDs recognized in step S15 in FIG. 14 have not beenreleased, it returns to step S99 in FIG. 18. The NFC communicationapparatus selects a new apparatus of interest from among targets whichhave not been completely released, that is, targets which havetemporarily released, and repeats similar processing.

If the NFC communication apparatus has determined in step S121 that allthe targets having the NFCIDs recognized have been completely released,it ends the process.

In steps S116 and S117 in FIG. 19, the command DEP_REQ and the responseDEP_RES are exchanged, whereby transmission and reception (dataexchange) of data are performed between the target and the initiator.This exchange of the command DEP_REQ and the response DEP_RES is onetransaction. After processing in steps S116 and S117, the NFCcommunication apparatus can return to step S114 through steps S118,S111, S112, and S113, and can change the communication parameter.Accordingly, the communication parameter concerning the communicationbetween the target and the initiator, such as the transfer rate, can bechanged for each transaction.

In steps S112 and S113, the initiator and the target exchange thecommand PSL_REQ and the response PSL_RES, whereby, in step S114, acommunication mode for the initiator and the target, which is one ofcommunication parameters, can be changed. Accordingly, the communicationmode for the target and the initiator can be changed for eachtransaction. This means that the communication mode for the target andthe initiator must not be changed during one transaction.

Next, the passive-mode-target process in step S38 in FIG. 15 isdescribed with reference to the flowchart in FIG. 20.

The NFC communication apparatus, which is a passive mode target, is inthe deselect state since it exchanges the command DSL_REQ and theresponse DSL_RES with the initiator, which is in the passive mode, insteps S37 and S38 in FIG. 15.

Accordingly, in step S131, the NFC communication apparatus determineswhether the command WUP_RES has been transmitted from the initiator. Ifit has determined that the command WUP_RES has not been transmitted, itreturns to step S131, and remains unchanged in the deselect state.

Alternatively, if the NFC communication apparatus has determined in stepS131 that the command WUP_REQ has been transmitted from the initiator,that is, when the NFC communication apparatus has received the commandWUP_REQ, it proceeds to step S131, transmits the response WUP_RES to thecommand WUP_REQ, and is waked up before proceeding to step S133.

In step S133, the NFC communication apparatus determines whether thecommand ATR_REQ has been transmitted from the initiator. If it hasdetermined that the above command has not been transmitted, it skipsover step S134 and proceeds to step S135.

Alternatively, if the NFC communication apparatus has determined in stepS133 that the command ATR_REQ has been transmitted from the initiator,that is, when the NFC communication apparatus has received the commandATR_REQ, it proceeds to step S135, and transmits the response ATR_RES tothe command ATR_RES before proceeding to step S135.

In step S135, the NFC communication apparatus determines whether thecommand DSL_REQ has been transmitted from the initiator. If the NFCcommunication apparatus has determined in step S135 that the commandDSL_REQ has been transmitted, that is, when the NFC communicationapparatus has received the command DSL_REQ, it proceeds to step S136.The NFC communication apparatus transmits the response DSL_RES to thecommand DSL_REQ, and returns to step S131. This sets the NFCcommunication apparatus to be in the deselect state.

Alternatively, if the NFC communication apparatus has determined in stepS135 that the command DSL_REQ has not been transmitted from theinitiator, it proceeds to step S137. The NFC communication apparatusdetermines whether the command PSL_REQ has been transmitted from theinitiator. If it has determined that the above command has not beentransmitted, it skips over steps S138 and S139 and proceeds to stepS140.

Alternatively, if the NFC communication apparatus has determined in stepS137 that the command PSL_REQ has been transmitted from the initiator,that is, when the NFC communication apparatus has received the commandPSL_REQ, it proceeds to step S138. The NFC communication apparatustransmits the response PSL_RES to the command PSL_RES, and proceeds tostep S139.

In step S139, the NFC communication apparatus changes its communicationparameter in accordance with the command PSL_REQ from the initiator, andproceeds to step S140.

In step S140, the NFC communication apparatus determines whether thecommand DEP_REQ has been transmitted from the initiator. If it hasdetermined that the above command has not been transmitted, it skipsover step S141 and proceeds to step S142.

Alternatively, if the NFC communication apparatus has determined in stepS140 that the command DEP_REQ has been transmitted from the initiator,that is, when the NFC communication apparatus has received the commandDEP_REQ, it proceeds to step S141. The NFC communication apparatustransmits the response DEP_RES to the command DEP_REQ, and proceeds tostep S142.

In step S142, the NFC communication apparatus determines whether thecommand PSL_REQ has been transmitted from the initiator. If it hasdetermined that the above command has not been transmitted, it returnsto step S133, and similar processing is subsequently repeated.

Alternatively, if the NFC communication apparatus has determined in stepS142 that the command PSL_REQ has been transmitted from the initiator,that is, when the NFC communication apparatus has received the commandPSL_REQ, it proceeds to step S143. The NFC communication apparatustransmits the response RSL_RES to the command RSL_REQ. This ends thecommunication with the initiator, and the process ends.

Next, FIG. 21 and FIG. 22 are flowcharts showing details of theactive-mode-initiator communication process in step S61 in FIG. 16.

In the passive-mode-initiator communication process illustrated in FIG.18 and FIG. 19, the initiator continuously outputs electromagneticwaves, while, in the active-mode-initiator communication process in FIG.21 and FIG. 22, the initiator initiates output of electromagnetic wavesby performing the active RFCA processing before transmitting a command,and performs processing (OFF processing) for stopping outputting theelectromagnetic waves after ending the transmission of the command.Excluding the above point, in the active-mode-initiator communicationprocess in FIG. 21, in each of steps S151 to S161, and steps S171 toS181 in FIG. 22, processing similar to the case of each of steps S91 toS101 in FIG. 18 and steps S111 to S121 in FIG. 19 is performed.Accordingly, its description is omitted.

Next, FIG. 23 is a flowchart showing details of the active-mode-targetcommunication process in step S79 in FIG. 17.

In the passive-mode-target communication process illustrated in FIG. 20,the target transmits data by performing load modulation onelectromagnetic waves output by the initiator, while, in theactive-mode-target communication process in FIG. 23, the targetinitiates output of electromagnetic waves by performing the active RFCAprocessing before transmitting a command, and performs processing (OFFprocessing) for stopping outputting the electromagnetic waves afterending the transmission of the command. Excluding the above point, inthe active-mode-target communication process in FIG. 23, in each ofsteps S191 to S203, processing similar to the case of each of steps S131to S143 in FIG. 20 is performed. Accordingly, its description isomitted.

Next, in communication by the NFC communication apparatus, for example,a communication protocol called NFCIP (Near Field CommunicationInterface and Protocol)-1 is employed.

FIG. 24 to FIG. 29 are illustrations of details of NFCIP-1 employed incommunication by the NFC communication apparatus.

Specifically, FIG. 24 is a flowchart illustrating common initializationand SDD processing performed by an NFC communication apparatus whichperforms communication based on NFCIP-1.

At first, in step S301, the NFC communication apparatus, which becomesan initiator, performs initial RFCA processing, and proceeds to stepS302. In step S302, the NFC communication apparatus, which becomes theinitiator, determines whether to have detected an RF field by theinitial RFCA processing in step S301. If the NFC communication apparatushas determined in step S302 to have detected the RF field, it returns tostep S301, and similar processing is subsequently repeated. In otherwords, while detecting the RF field, the NFC communication apparatus,which becomes the initiator, forms no RF field so as not to interferewith communication by another NFC communication apparatus, which formsthe RF field.

Alternatively, if the NFC communication apparatus has determined in stepS302 not to have detected the RF field, it proceeds to step S303, andperforms, in the initiator state, communication mode and transmissionmode selection, etc.

Specifically, in the case of performing passive mode communication, theNFC communication apparatus proceeds from step S302 to step S303-1between steps S303-1 and S303-2 forming step S303, changes thecommunication mode to the passive mode in the initiator state, andselects a transfer rate. Also, in step S303-1, the NFC communicationapparatus, which becomes the initiator, performs initialization and SDDprocessing, and proceeds to step S304-1 between steps S304-1 and S304-2forming step S304.

In step S304-1, the NFC communication apparatus is activated (starts) inthe passive mode, and proceeds to step S305.

Alternatively, in the case of performing active mode communication, theNFC communication apparatus proceeds from step S302 to step S303-2between steps S303-1 and S303-2 forming step S303, changes thecommunication mode to the active mode in the initiator state, selectsthe transfer rate, and proceeds to step S304-2 between steps S304-1 andS304-2 forming step S304.

In step S304-2, the NFC communication apparatus is activated in theactive mode and proceeds to step S305.

In step S305, the NFC communication apparatus selects the communicationparameter required for communication and proceeds to step S306. In stepS306, the NFC communication apparatus performs data exchange(communication) based on a data exchange protocol in accordance with thecommunication parameter selected in step S305, and ends the dataexchange before proceeding to step S307. In step S307, the NFCcommunication apparatus is deactivated and ends the transaction.

The NFC communication apparatus can be set by default to be, forexample, a target. The NFC communication apparatus, which is set to bethe target, forms no RF field, and is on standby until a command istransmitted from the initiator (until the initiator forms an RF field).

Also, the NFC communication apparatus can become an initiator, forexample, in accordance with a request from an application. For example,an application can determine which of the active mode and the passivemode the communication mode is, and can select (determine) the transferrate.

The NFC communication apparatus, which becomes the initiator, forms anRF field if no RF field is formed in the exterior, and the target isactivated by the RF field formed by the initiator.

After that, the initiator transmits a command in the selectedcommunication mode and transfer rate, and the target sends back aresponse (responds) at a communication mode and transfer rate identicalto those of the initiator.

Next, FIG. 25 is a flowchart illustrating initialization and SDDperformed by the NFC communication apparatus, which becomes theinitiator.

At first, in step S311, the initiator transmits the command SENS_REQ forsearching for a target existing in the RF field formed by the initiator,and proceeds to step S312. In step S312, the initiator receives theresponse SENS_RES to the command SENS_REQ, which is transmitted from thetarget existing in the RF field formed by the initiator, and proceeds tostep S313.

In step S313, the initiator confirms the content of the responseSENS_RES from the target which is received in step S312. In other words,the response SENS_RES includes pieces of information of NFCID1 size bitframe and bit frame SDD. In step S313, the initiator confirms thecontents of the pieces of information.

After that, proceeding from step S313 to S314, the initiator selectscascade (transfer) level 1 and executes SDD. Specifically, in step S314,the initiator transmits the SDD requiring command SDD REQ, and transmitsthe command SEL_REQ to request selection of a target. In the commandSEL_REQ, information representing the present cascade level is located.

The initiator waits for the response SEL_RES to the command SEL_REQ tobe transmitted from the target, receives the response SEL_RES, andproceeds from step S315 to S316.

Here, the response SEL_RES includes any one of information indicatingthat the target does not end the communication based on NFCIP-1,information indicating that the target meets an NFC transport protocoland ends the communication based on NFCIP-1, and informationrepresenting that the target does not meet the NFC transport protocoland ends the communication based on NFCIP-1.

In step S316, by confirming the content of the response SEL_RES receivedfrom the target, the initiator determines which of the informationindicating that the target does not end the communication based onNFCIP-1, the information indicating that the target meets the NFCtransport protocol and ends the communication based on NFCIP-1, and theinformation representing that the target does not meet the NFC transportprotocol and ends the communication based on NFCIP-1, is included in theresponse SEL_RES.

If the initiator has determined in step S316 that the response SEL_RESincludes the information indicating that the target does not end thecommunication based on NFCIP-1, it proceeds to step S317, and increasesthe cascade level from the present value. The initiator returns fromstep S317 to S315, and subsequently repeats similar processing.

Also, if the initiator has determined in step S316 that the responseSEL_RES includes the information indicating that the target meets theNFC transport protocol and ends the communication based on NFCIP-1, theinitiator ends the communication based on NFCIP-1 and proceeds to stepS319. In step S319, the initiator transmits the command ATR_REQ.Subsequently, communication using the commands and responses shown inFIG. 12 is performed between the initiator and the target.

In addition, if the initiator has determined in step S316 that theresponse SEL_RES includes the information representing that the targetdoes not meet the NFC transport protocol and ends the communicationbased on NFCIP-1, the initiator ends the communication based on NFCIP-1and proceeds to step S318. In step S318, the initiator performscommunication using its own commands and protocol with the target.

Next, FIG. 26 is a timing chart illustrating initialization performed inthe active mode by the initiator and the target.

After performing initial RFCA processing in step S331, the initiatorproceeds to step S332 and forms an RF field (sets the RF field to beon). In step S332, the initiator transmits a command (Request), andstops the formation of the RF field (sets the RF field to be off). Here,in step S332, the initiator selects, for example, a transfer rate andtransmits the command ATR_REQ at the transfer rate.

At the same time, in step S333, the target detects the RF field formedin step S332 by the initiator, and receives the command transmitted bythe initiator before proceeding to step S334. In step S334, the targetperforms response RFCA processing, waits for the RF field formed by theinitiator to be off, and proceeds to step S335. The target sets the RFfield to be on. In step S335, the target transmits a response to thecommand received in step S333, and sets the RF field to be off. Here, instep S335, the target transmits, for example, the response ATR_RES tothe command ATR_REQ transmitted from the initiator at a transfer rateidentical to that for the command ATR_REQ.

The response transmitted in step S335 by the target is received by theinitiator. Proceeding from step S336 to S337, the initiator performsresponse RFCA processing, waits for the RF field formed by the target tobe off, and proceeds to step S337 to set the RF field to be on. Inaddition, in step S337, the initiator transmits a command and sets theRF field to be off. Here, in step S337, the initiator can transmit thecommand PSL_REQ in order to change, for example, a communicationparameter. In step S337, by transmitting, for example, the commandDEP_REQ, the initiator can initiate data exchange based on a dataexchange protocol.

The command transmitted in step S337 by the initiator is received by thetarget. Subsequently, similar communication between the initiator andthe target is performed.

Next, a passive-mode activation protocol is described with reference tothe flowchart in FIG. 27.

At first, in step S351, the initiator performs initial RFCA processing,and proceeds to steps S352 and sets the communication mode to thepassive mode. Proceeding to step S353, the initiator performsinitialization and SDD and selects a transfer rate.

After that, proceeding to step S354, the initiator determines whether torequest an attribute from the target. If the initiator has determinednot to request the attribute from the target in step S354, it proceedsto step S335. The initiator performs communication with the target inaccordance with its own protocol. It returns to step S354 and repeatssimilar processing.

Alternatively, if the initiator has determined in step S334 to requestthe attribute from the target, it proceeds to step S356. The initiatortransmits the command ATR_REQ. This requests the attribute from thetarget. The initiator waits for the response ATR_RES to the commandATR_REQ to be transmitted from the target, and proceeds to step S357.The initiator receives the response ATR_RES and proceeds to step S358.

In step S358, based on the response ATR_RES received from the target instep S357, the initiator determines whether the communication parameter,that is, for example, the transfer rate, can be changed. If theinitiator has determined in step S358 that the transfer rate cannot bechanged, it skips over steps S359 and S361 and proceeds to step S362.

Alternatively, if the initiator has determined in step S358 that thetransfer rate can be changed, it proceeds to step S359. The initiatortransmits the command PSL_REQ. This request the target to change thetransfer rate. The initiator waits for the response PSL_RES to thecommand PSL_REQ to be transmitted from the target, and proceeds fromstep S359 to S360. The initiator receives the response PSL_RES, andproceeds to step S361. In step S361, in accordance with the responsePSL_RES received in step S360, the initiator changes the communicationparameter, that is, for example, the transfer rate, and proceeds to stepS362.

In step S362, the initiator exchanges data with the target in accordancewith a data exchange protocol. After that, the initiator proceeds tostep S363 or S365.

In other words, when the initiator sets the target to be in the deselectstate, it proceeds from step S362 to S363 and transmits the commandDSL_REQ. The initiator waits for the response DSL_RES to the commandDSL_REQ to be transmitted from the target, and proceeds from step S363to S364. After receiving the response DSL_RES, the initiator returns tostep S354 and subsequently repeats similar processing.

At the same time, when completely ending the communication with thetarget, the initiator proceeds from step S362 to S365, and transmits thecommand RLS_REQ. The initiator waits for the response RLS_RES to thecommand RLS_REQ to be transmitted from the target, and proceeds fromstep S365 to S366. After receiving the response RLS_RES, the initiatorreturns to step S351, and subsequently repeats similar processing.

Next, an active-mode activation protocol is described with reference tothe flowchart in FIG. 28.

At first, in step S371, the initiator performs initial RFCA processing,and proceeds to step S372. The initiator sets the communication mode tothe active mode. Proceeding to step S373, the initiator transmits thecommand ATR_REQ. This requests an attribute from the target. Theinitiator waits for the response ATR_RES to the command ATR_REQ to betransmitted from the target, and proceeds to step S374. The initiatorreceives the response ATR_RES, and proceeds to step S375.

In step S375, based on the response ATR_RES received from the target instep S374, the initiator determines whether the communication parameter,that is, for example, the transfer rate, can be changed. If theinitiator has determined in step S375 that the transfer rate cannot bechanged, it skips over steps S376 to S378 and proceeds to step S379.

Alternatively, if the initiator has determined in step S375 that thetransfer rate can be changed, it proceeds to step S376, and transmitsthe command PSL_REQ. This requests the target to change the transferrate. The initiator waits for the response PSL_RES to the commandPSL_REQ to be transmitted from the target, and proceeds from step S376to S377. The initiator receives the response PSL_RES, and proceeds tostep S379. In step S378, in accordance with the response PSL_RESreceived in step S377, the initiator changes the communicationparameter, that is, for example, the transfer rate, and proceeds to stepS379.

In step S379, in accordance with a data exchange protocol, the initiatorexchanges data with the target. After that, the initiator proceeds tostep S380 or S384, if needed.

In other words, when the initiator sets the target, with which it iscommunicating, to be in the deselect state, and wakes up any of targets,which have already been in the deselect state, it proceeds from stepS379 to S380, and transmits the command DSL_REQ. After the initiatorwaits for the response DSL_RES to the command DSL_REQ to be transmittedfrom the target, it proceeds from step S380 to S381, and receives theresponse DSL_RES. Here, the target, which has transmitted the responseDSL_RES, is set to be in the deselect state.

After that, proceeding from step S381 to S382, the initiator transmitsthe command WUP_REQ. After the initiator waits for the response WUP_RESto the command WUP_REQ, it proceeds from step S382 to S383, receives theresponse WUP_RES, and returns to step S375. Here, the target, which hastransmitted the response WUP_RES, is waked up, and the waked-up targetis subject to processing in step S375 and thereafter which is performedby the initiator.

In addition, when completely ending the communication with the target,the initiator proceeds from step S379 to S384, and transmits the commandRLS_REQ. After the initiator waits for the response RLS_RES to thecommand RLS_REQ to be transmitted from the target, it proceeds from stepS384 to S385, and receives the response RLS_RES before returning to stepS371. The initiator subsequently repeats similar processing.

Next, FIG. 29 shows NFCIP-1 protocol commands for use in NFCIP-1 andresponses to the commands.

The commands and responses shown in FIG. 29 are identical to thecommands and responses shown in FIG. 12. However, FIG. 12 shows only themnemonics of the commands and responses, but FIG. 29 shows, not onlymnemonics, but also definitions of the commands.

The commands ATR_REQ, WUP_REQ, PSL_REQ, DEP_REQ, DSL_REQ, and RLS_REQare transmitted by the initiator, and the responses ATR_REQ, WUP_RES,PSL_RES, DEP_RES, DSL_RES, and RLS_RES are transmitted by the target.

However, the command WUP_REQ is transmitted only when the initiator isin the active mode, and the response WUP_RES is transmitted only whenthe target is in the active mode.

In this specification, processing steps which describe processingperformed by an NFC communication apparatus do not always need to betime-sequentially performed in the order shown as flowcharts, butinclude steps executed in parallel or separately (For example, parallelprocessing or object-based processing).

INDUSTRIAL APPLICABILITY

As described above, the present invention enables various types of nearfield communication.

1. A communication system of performing, by first and second dataprocessing apparatuses, electromagnetic-induction communication using acarrier having a single frequency, wherein: the first and second dataprocessing apparatuses each comprises: modulating means for modulatingthe carrier into a signal of data to be transmitted at one of aplurality of transfer rates; and demodulating means for demodulating asignal of data transmitted at one of a plurality of transfer rates; atransfer rate for use between the first and second data processingapparatuses is changeable in one transaction; each apparatus of thefirst and second data processing apparatuses has, as communicationmodes, an active mode in which the apparatus transmits data byoutputting a carrier; and a passive mode in which one data processingapparatus of the first and second data processing apparatuses transmitsdata by outputting a carrier, while the other data processing apparatustransmits data by performing load modulation on the carrier output bysaid one data processing apparatus; and data transmission is performedby using any communication mode of the active mode and the passive mode,the communication mode being maintained during at least one transaction.